<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        *{
          margin:0;
          padding:0;  
        }
        .wrapper{
            width:100%;
            height: 300px;
            border:1px solid black;
        }
        .content{
            float: left;
            width:50%;
            height: 100px;
            background: aquamarine;

        }
        .content:first-of-type{
            background: orange;
            border:10px solid blue;
            box-sizing: border-box;
        }
    </style>
</head>
<body>
    <div class="wrapper">
        <div class="content"></div>
        <div class="content"></div>
    </div>
</body>
</html>